Process for producing hydroxy aldehydes and hydroxy ketones



Patented Jan. 13, 1942 UNITED STATES PATENT OFFICE" PROCESS FORPRODUCING .HYDROXY ALDEHYDES AND HYDROXY KETONES William E. Hanford andRichard S. Schreiber, Wilmington, DeL, assignors to E. Ldu Pont deNemours & Company, Wilmington, Del., a.

corporation of Delaware Application February 27, 1940, Serial No.320,988

Claims.

This invention relates to the continuous single phase process forconverting formaldehyde to hydroxy aldehydes and hydroxy ketones.

It is 'well known that in the self-condensation of formaldehyde thereare two competing reactions: one yielding hydroxy aldehydes and hydroxyketones, and the other a Cannizzaro reaction involving the formation offormic acid and methanol. 0. Loew (J. Prakt. Chem. 34, 51 (1886)), oneof the earliest workers in this field,

states that a considerable amount of formic acid and methanol are formedif the formaldehyde concentration exceeds 1 to 2 per cent, regardless Iexpedient is not a practical solution to the problem (1) for economicreasons since it involves replacement of a cheap solvent by a relativelyexpensive solvent, (2) because it introduces complicating sidereactions, e. g., acetal and ether formation, and (3) because thecondensation reaction goes faster in water than in alcohol.

W. E. Hanford and R. S. Schreiber in their copending application, SerialNo. 226,730, filed Aug. 25, 1938, describea process for condensingformaldehyde in aqueousmedia in concentrations exceeding 8 per cent togive high yields of hydroxyaldehydes'and hydroxy ketones. The preferred,method described in said application is a batchwise operation and,while it has the advantage that sumcient time may be allowed for theformaldehyde to reach the desired degree of condensation, it has thedisadvantage that the method is discontinuous and hence more costly thanif the equipment could bekept in constant use. In order to operate acontinuous process, however,

the catalyst must be in solution during the reac-" tion. Solublecatalysts of the prior art that had been used in carrying out thecondensation of formaldehyde solutions of less than 5% concentrationswere found to be inoperative with the higher concentrations offormaldehyde.

It is accordingly an object of this invention to provide a practicalprocess for condensing formaldehyde by a continuous single phase flowmethod. A further object is the continuous-single phase conversion offormaldehydes tohydroxy aldehydes and hydroxy ketones. Another object Iis to solubilize a catalyst selected from the elements of group IV ofthe periodic table so as to obtain a homogeneous solution. A stillfurther object is the continuous single phase conversion of formaldehydeto high yields of low molecular weight hydroxy aldehydes and hydroxyketones. Other objects will be apparent from the reading of thefollowing description of the invention.

These objects are accomplished by one or more of the steps of theprocess which comprise dissolving a compound of an element of group IVof the periodic table having an atomic number in the range of 50 to 90in an enediol solution having a pH of about 5 or more, adding saidsolution to an aqueous formaldehyde solution of at least 8% formaldehydeconcentration, and condensing the resulting mixture by heat treatment soas to convert the forma'ldehyde to hydroxy aldehydes and hydroxyketones, stopping the conversion when the desired degree of condensationhas been obtained and removing the catalyst, and recovering the hydroxyaldehydes and hydroxy ketones.

The invention may best be understoodby reference to the accompanyingdrawing which is a' flow sheet of a preferred embodiment of thisinvention. Referring to the drawing tanks A, B, and C containrespectively a solution of a caustic alkali, enediols, and a catalyst.These three components are allowed to flow into the mixing tank D insuch proportions that when they are properly admixed there will becomplete solution of the catalyst. This solution is allowed to flow totank H where it becomes admixed with a formal dehyde compound-watersolution from tank G. Tank G is a mixing tank which receivesformaldehyde compound from tank E and water from tank F in ratios so as.to obtain the desired con- I centration of formaldehyde compound andwater.

ber. The reaction mixture may then be cooled by passing through acooling unit J. From the cooling unit J the mixture may pass into thechamber L where it is admixed with an acid supplied from tank K. Thisacid is added insuch an amount as to cause precipitation of thecatalyst, which catalyst is removed by the filter M and recycled to tankC. The solution of hydroxy aldehydes and hydroxy. ketones passes fromthe filter M to the storage tank N. Part of the solution is recycled totank B to be used as an enediol source. The remaining solution iswithdrawn for processing to recover its various desired components. Ifdesired, a relatively constant pH may be maintained throughout thecondensation by continuous or intermittent addition of alkali at anumber of points in the reaction chamber as indicated in the diagram bythe addition of alkali from tank tothe reaction chamber.

The following examples set forth certain well defined instances of theapplication of this invention. They are, however, not to be consideredas limitations thereof, since many modifications may be made withoutdeparting from the spirit and scope of this invention.

Example I 315 g. of paraformaldehyde were dissolved in 350 g. of waterby warming to 80 C. with a trace of alkali. To this formaldehydesolution was then added 30 g. of lead sulfate Whichhad previously beensolubilized by suspending in 90 cc. of a solution containing 40 g. ofenediols and adding 100 cc. of per cent sodium hydroxide while keepingthe solution cold. This solution was then passed through a nickel coil(T e inch in diameter and feet long and having a capacity of 75 cc.) ata rate of 4 cc. per minute while maintaining a temperature of 90 to 95C. Under these conditions '75 per cent of the formaldehyde was condensedto hydroxy aldehydes and hydroxy ketones. The pH of the solution wasthen dropped to 5.0 by the addition of 2 cc. of concentrated sulfuricacid in 10 cc. of water and the solution filtered to remove theprecipitated lead sulfate. On testing a portion of the filtrate withhydrogen sulfide it was found that all of the lead ions had been removedby this treatment. "The pH of the solution was then raised to 7.1 by theaddition of 10 per cent sodium hydroxide and a sample containing 92 g.of the condensate as hydrogenated at 120 C. with 20 g. ofnickel-onkieselguhr catalyst and at pressures of 600 to 650 atmospheres.After filtering to remove the hydrogenation catalyst, the solution,which gave a negative test for reducing substances with Fehlingsolution, was distilled under reduced pressure to yield the followingresults:

Table I Fraction Grams Substance Yield 1 7.0 Ethylene glycol l0. 0 2 9.1Glycerol l3. 0 3 11.5 Erythritol 16.5

The yields are based on the formaldehyde condensed.

Example II 630 g. of paraformaldehyde were dissolved in 700 g. of Waterby warming to 80 C. with a trace 'of alkali. To this formaldehydesolution was at the rate of 1.7 cc. per minute, while maintain-' ing atemperature of 95 C. Under these conditions 72 per cent of theformaldehyde was polymerized to a mixture of hydroxy aldehydes andhydroxy ketones. The pH of the reaction mixture was then lowered to 4.0by the addition of 4 cc. of a. concentrated sulfuric acid in 10 cc. ofwater. A 240 cc. sample of this material which contained g. ofcondensate was hydrogenated with 20 g. of nickel-on-kieselguhr catalystin the manner described in Example 1. After removal of the hydrogenationcatalyst by filtration, the hydrogenated solution was distilled underreduced pressure to yield the following results:

Table II Fraction Grams Substance Yield 1 19.0 Methanol 21.0 8. 8 l3. 014. 5 cer 22. 5 7.0 Erythritol 10.7

The yields are based on the formaldehyde condensed.

Example III 316 g. of paraformaldehyde were dissolved in 350 g. of waterby warming to 80 C. with a trace of alkali. To this formaldehydesolution was then added 30 g. of stannous chloride which had previouslybeen dissolved by suspending in 100 cc. of the solution containing 125g. of enediols and adding 250 cc. of 10 per cent sodium hydroxide whilekeeping the solution cold. This mixture was then passed through thereaction coil described in Example I at a rate of approximately 1.4 cc.'per minute and at a temperature of C. Under ,these conditions 87 percent of the formaldehyde was polymerized to a mixture ofhydroxyaldehydes and hydroxy ketones. Without attempting to remove thecatalyst the pH was raised to 7.0 by the addition of 10 per cent sodiumhydroxide and then a 215 cc. sample containing 80 g. of condensate washydrogenated Table I I I Fraction Grams Substance The yields are basedon the formaldehyde condensed.

' Example IV 316 g. of paraformaldehyde were dissolved in 250 g. ofwater by warming to 80 C. with a trace of alkali. To this solution wasthen added a mixture containing 30 g. of cerium trichloride, cc. of asolution containing 40 g, of enediols and cc. of 10 per cent sodiumhydroxide. This solution was then passed through the reaction coildescribed in Example I at a rate of 0.5 cc. per minute and at atemperature of 95 C. Under these conditions 30 per cent of theformaldehyde was polymerized to a mixture of hydroxy aldehydes andhydroxy ketones.

Although in the foregoing examples paraformaldehyde has been usedexclusively, it is to be understood that in the practice of thisinvention any form of formaldehyde or any formaldehyde derivativecapable of liberating formaldehyde under the reacting conditions may beused. To depolymerize paraformaldehyde or trioxymethylene it is notessential to add an alkali as the para formaldehyde or trioxymethylenedepolymerize by merely heating at 90 C. or above for a short time.Formaldehyde solutions in which the concentration is in ,excess of 8percent can be employed in this process.

The preferred catalysts for this process are lead hydroxide, lead oxide,lead formate, lead sulfate, lead oxalate, tin formate and tin chloride.In place of the preferred catalyst, however, pracas a catalyst isillustrated in Example IV. The amount of catalyst required for efficientoperation of this process depends to some degree on several factors suchas concentration of formaldehyde, the temperature used, the hydrogen ionconcentration of the mixture, the amount and type of alkali used to.solubilize the catalyst and the concentration of enediols employed.While amounts of catalysts as low as 0.01 per cent may be used, it isgenerally preferred not to use less than 0.15 per cent'based on theformaldehyde reaction .is sluggish and incomplete.

Although in the examples cited above, sodium hydroxide was usedexclusively, any strong alkaline reacting substance will work equallywell. For example, besides sodium hydroxide, potassium hydroxide,calcium hydroxide, trimethylamine, pyridine, triethylamine, and bariumhydroxide can be employed with a high degree of success. Although theamount of alkali employed depends on a variety of factors such asconcentration of catalyst, concentration of enediols, and temperatureemployed, itis generally preferred to use not less than'2 per cent basedon the amount of formaldehyde used.

By enediols is meant compounds having the grouping ta $3 or compoundswhich are capable of enolizing, rearranging, or hydrolizing to giveproducts having such grouping. Among such products are glucose, ascorbicacid, fructose, erythrose, reductone, aldehydes and hydroxy ketonesproduced by condensation of formaldehyde, which consists essentially ofglycolic and glyceric aldehydes, tetroses, pentoses, hexoses; along withsome unchanged formaldehyde. The amounts of enediols or theirequivalents which are most effective range from one to about 10 percent, based on the formaldehyde. The use of more than 10 per cent ofenediols or their equivalents usually ofiers no advantage.

If desired, the reaction may be initiated at temperatures from about 25C. to about 150 C. and at pH within the range of 2.5 to 10.0. It isgenerally preferred, however, to operate in a pH range of 5.0 to 9.0 andat temperatures of 45 C.

because when too small amounts are used, the

invert sugar, and a mixture of hydroxy tically any compound of lead,tin, thorium, or cerium may be used. The use of cerium chloride droxyketones (i. e., glycolic aldehyde, glyceric aldehyde. dihydroxy acetone,erythroses, pentoses and hexoses) the condensation reaction stopped whenfrom 40 to 95% of the. formaldehyde has been condensed, preferably 60 to90%. This control in condensation may be obtained by regulating the fiowof the reactants through the reactionzone or by stopping the reaction byacidifying the reactants or by cooling same. Any combination of thesemethods may also be used in preventing further reaction. Temperatures offrom 0 to 15 C. have been found to be practical. In acidifying thesolution any mineral acid, or strong organicacid, maybe used. The use ofsuch acids as sulfuric and oxalic are particularly practical when leadand tin compounds have been used as catalysts. These acidspermit theformation of insoluble sulfates and oxalates that I are easily removedby filtration. In the addition of these acids sumcient quantity of sameshould be added so that the pH of the solution is dropped to 5 or below..The precipitated compound is then filtered or removedby decantation orcentrifuging and may be re-used.

The hydroxy aldehydes and hydroxy ketones obtained'by this process maybe used as intermediates in the synthesis of valuable industrialproducts or may be catalytically hydrogenated by any method, eitherbatch or continuous, adaptable for the catalyt c hydrogenation ofunsaturated oxygen-to-carbon linkages. It is pr'ev fered, however, tocarry out the hydrogenation of the products as obtained in this processby the method described in the copending application of Hanford andSchreiber, SerialNo. 226,- 731. filed August 25, 1938. o

The products obtained by this process are val uable intermediates forthe preparation of polyhydroxy compounds which find extensive use assofteners for Cellophane, as polymer ingredients, etc. Th polyhydroxyaldehydes and polyhydroxy ketones may be used as such to yield polymericproducts by condensing with bifunctional compounds.

This invention represents a distinct advance in the ar since it providesa means forcondensing formaldehyde continuously in a single phase systemto hydroxy aldehydes and hydroxy ketones. Up to this time no method wasavailable for obtaininghomogeneous solutions which contained all thenecessary reactants for condensing formaldehyde.

We claim:

1. A continuous process for the production of hydroxyaldehydes andhydroxy ketones which comprises dissolving a compound of an element of.the 4th group of the periodic tableln' an enediol by maintaining the pHof the enediol in ex-' to 105 C. If desired, a constant pH may be ofhigh yield of low molecular weight hydroxyaldehydes suchas glycolic andglyceric.

In order to'produce high yields of the lower molecular weight hydroxyaldehydes and hycess of 5 and adding the resulting solution to anaqueous solution of formaldehyde, passing the mixture through a reactionchamber heated to a temperature between 25 and 150 C.-, stopping thereaction when the desired degree of condensation is attained, andrecovering the desired hydroxyaldehydes and hydroxy ketones.

2. The process in accordance with claim 1. characterized in that the pHis maintained relatively constant in the reaction chamber by the addingof alkali to the reactants as they pass through said chamber. I v

3. A process for the production of hydroxyaldehydes and hydroxy ketoneswhich comprises passing in a continuous manner an aqueous solutioncontaining at least 8%, formaldehyde together with an enediol and acompound of an element of the fourth group of the periodic table througha reaction chamber heated to a tem- 5. The process in accordance withclaim 3' characterized in that the rate of passage through the reactionchamber is adjusted so as to obtain from 45% to 95% condensation offormaldehyde. t V

6. A process for the production of hydroxyaldehydes and hydroxy ketoneswhich comprises passing in a continuous manner an aqueous solutioncontaining at least 8% formaldehyde together with an enediol and acompound of an element of the fourth group of the periodic table througha reaction chamber heated to a temperature between 50 and 150 C. andstopping the reaction when from 45% to 95% of the formaldehyde has beencondensed by cooling the reaction to a temperature of C. to C.

7. A process for the production of hydroxyaldehydes and hydroxy ketoneswhich comprises ment of the fourth group of the periodic table isselected from the group'consisting of lead and tin and the acid added tostop the reaction is selected from the group consisting of oxalic acidand sulfuric acid.

9. A continuous process for.the production of hydroxyaldehydes andhydroxy ketones which comprises dissolving lead sulfate in an aqueousenediol solution by maintaining said solution at a pH of at least"? andadding the resulting solution to an aqueous solution of formaldehyde ofat least 8% concentration, passing the mixture through a reactionchamber heated to a temperature between 50 and 150 0., and stoppingpassing in a continuous manner an aqueous solution containing at least8% formaldehyde together with an enediol and a compound of an element ofthe fourth group of the periodic table through a reaction chamber heatedto a temperature between and 150 C. and stopping the reaction whenfrom',45% to of the formaldehyde has been condensed by adding an acid tosaid reactants in an amount suflicient to reduce the pH of the solutionto at least 5.0.

8. The process in accordance with claim 7 characterized in that thecompound of the elethe reaction when from 45% to 95% of the aldehyde hasbeen condensed by adding to the reactants sulfuric acid in an amountsuflicient to reduce the pH of the solution to at least 5, separatingthe lead sulfate formed by precipitation and recycling same andrecovering from the reaction mass hydroxyaldehydes and hydroxy ketones.

10. A continuous process for the production of hydroxyaldehydes andhydroxy ketones which comprises passing through a reaction chamber amixture of formaldehyde in aqueous solution and enediol and a compoundof an element of the fourth group of the periodic table and maintainingthe pH of said solution relatively constant at a, pH in excess of 5 byadding alkali to the reactants as they pass through said chamber, theprocess being further characterized in that the reaction chamber isoperated at a temperature between 25 and C.

WILLIAM E. HANFORD. RICHARD S. SCI-IREIBER.

